Greenhouse StructuresGreenhouse Structures

Steven E. Newman, Ph.D.Colorado State University Cooperative ExtensionHorticulture and Landscape Architecture

Glass Greenhouses

• Glass was the only choice until the 1950s• Advantages

– Greater light intensity over plastic panels and film plastic– More air exchanges with glass

• Lower relative humidity• Less disease• Greater evapotranspiration

Glass Greenhouses

• Disadvantages– More “leaks” – greater heat input– Higher initial cost compared to plastic

• Initial cost vs. long-term• Maintenance• Plastics require recovering

Glass Greenhouses

• Lean-to– Placed against an existing

wall– Typically facing south– Common for institutional or

hobby greenhouses

Glass Greenhouses

• Even-span– Two slopes of equal pitch

and width– Most common

configuration

Glass Greenhouses

• Uneven-span– Roofs of unequal width and

pitch– Adaptable to slopes– Good for high latitude sites

Glass Greenhouses

• Ridge and Furrow– Multiple A-frame spans

connected along the eaves– Gutters placed at junction

of eaves– Also termed gutter connect

Glass Greenhouses

• Frame types– Wood frames

• < 20 ft. wide– Pipe Frames

• Up to 40 ft. wide• Side posts, columns, cross

ties, and purlins from pipe

Pipe Frame Greenhouses

Glass Greenhouses

• Truss frames– Flat steel, tubular steel, or

angle iron used to form truss

– Most glass houses use truss frames

Glass Greenhouses

• Glass attachment– Placed upon sash bars with putty– Most sash bars are aluminum

• Stronger = less superstructure per unit of glass• Reflective = more light than painted wood• Less maintenance than wood

Sash Bars

Glass Greenhouses

• Glass types– 16-inch up to 39-inch pane widths

• Wider panes = more light• Mainly double strength

– Float glass is mainly used in U.S.• 88% light transmission

– Low iron glass • 90-92% light transmission• More expensive

Glass Greenhouses

Glass Greenhouses

• Tempered glass allows wider panes• Up to 6 by 13 feet• Bent to a curve• Fewer seals between eaves and ridges• Can be bent to a curve

Glass Greenhouses

Tempered Glass

Glass Greenhouses

• Roof styles– Low profile roof– Venlo– Single panes from eaves to

ridge– Smaller pitch angle– Less roof area– Less heating cost

Glass Greenhouses

• Roof styles– High profile– Large pitch angle

• 6 x 12– Large roof area– Greater heating costs

Hail Damage

Hail Damage

Snow Damage

Film Plastic Greenhouses

Film Plastic Greenhouses

Polyethylene• Major film used in U.S.• 6-mil exterior

– 4-mil interior– Double layer for insulation

• UV inhibitors to increase life span– 3-5 year life– Anti-fog materials to prevent condensation– IR blockers = less heat loss

Film Plastic Greenhouses

• IR blockers to prevent heat loss– Short wave energy into

greenhouse– Surfaces radiate IR

radiation– Films block re-radiation

Film Plastic Greenhouses

Polyester• Mylar• Too expensive for glazing,

but is used for shade cloth materials

• Retractable roof material

Film Plastic Greenhouses

Frame Types• A-frame not the best (hard to cover)

Film Plastic Greenhouses

Frame Types• Quonset

– Bent bows using steel pipe or square steel tubing

– 20-30 ft. width– Ground to ground

Film Plastic Greenhouses

Frame Types• Gutter-connected• Sidewalls of 8-14 feet• Can be roll-up• Usually rigid plastic• Quonset-arch• Gutters

– 6-inch/100-ft slope

Film Plastic Greenhouses

Frame Types• Gutter-connected venting

Film Plastic Greenhouses

Frame Types• Saw tooth venting

Film Plastic Greenhouses

Double-layer Covering• Two layers with air pocket in

between• Attached with clamping

channel or batten strips

Polylock

Film Plastic Greenhouses

Reinforcedpolyethylene

Film Plastic Greenhouses

Double-layer Covering• Plastic expands and contracts with temperature

changes– Leave 2-3 inches or more when warm– Pull plastic tight when cold

• Air space (inflated)– 4-inches– Not too much – Not too little

Inflation Fan

Rigid-Plastic Greenhouses

Fiberglass Reinforced Plastic (FRP)• Less popular in the past• Flexible and can be bent over a Quonset frame• More resistant to glass to breakage• More light diffusion than glass

Rigid-Plastic Greenhouses

Fiberglass Reinforced Plastic (FRP)• Surface easily abraded

– Results in a pitted surface– Frayed fibers “bloom”– Gather dirt and debris

• Transmits 88% PAR • Light – less structure

Rigid-Plastic Greenhouses

Fiberglass Reinforced Plastic (FRP)

Rigid-Plastic Greenhouses

Fiberglass Reinforced Plastic (FRP)

Rigid-Plastic Greenhouses

Fiberglass Reinforced Plastic (FRP)• Bows / trusses / rafters placed 8 to 10 feet apart• Distance between purlins is dependent on:

– Weight of FRP used– Live load

• FRP is very flammable

Rigid-Plastic Greenhouses

Polycarbonate• Considered relatively new• 10-year life span guarantee• Widely used to glaze end walls and gables of Quonset houses• Easily retrofitted to glass houses• High impact resistance• UV protectant added to most products

Rigid-Plastic Greenhouses

Polycarbonate• Available as:

– Corrugated– Double wall– Triple wall

• PAR light transmission about 79%

• Not considered flammable

Rigid-Plastic Greenhouses

Extruded aluminum locks and seals

Rigid-Plastic Greenhouses

Rigid-Plastic Greenhouses

Acrylic• Good PAR transmission – 83%• Very flammable• Guaranteed for 10 years• More resistant to breakage than glass, but less than

polycarbonate• Attachment similar to polycarbonate

Orienting a Greenhouse

• Want to maximize light (and uniformity of light)– Percent light entering a greenhouse depends on “angle of

incidence”• Angle that a light ray striking a surface makes with a line

perpendicular to the surface• An angle of incidence=0° allows the most light to enter the surface• Reflective loss increases as AOI increases (up to 90°)

Reflection

Orienting a Greenhouse

• Above 40° latitude:– Run ridges of single-span houses E-W to maximize light

intensity– Run ridges of multi-span houses N-S for light distribution

• Must accept lower winter light transmission to avoid shadow pockets

• N-S ridge and gutter shadows “move” but E-W shadows do not

Angle of Incidence

Orienting a Greenhouse

• Below 40° latitude:– Run ridges of all houses N-S– Better light distribution (moving shadows) is more important

than light transmission optimization– Remember: WINTER light is the factor

Angle of Incidence

Greenhouse Floor Plans

• Plan for “ultimate size”• Plan for materials and product movement

– Height of carts– Width for passing carts– Paved aisles / monorails

Carts

Layout

Monorails

Conveyer

Conveyers

Conveyer

Basket Lines

Moving Tables

Cut Flower Beds

Height dependent• Tall crops

– Typically grown on or in the ground

– Roses, carnation, tomatoes, and peppers

Cut Flower Beds

Height dependent• Medium height crops• May be grown in raised

benches• Consider harvest techniques• Chrysanthemums,

snapdragons, and lilies

Cut Flower Beds

Height dependent• Some crops require trellising

– Tall crops require wire supports to prevent crooked stems

– Select material allowing easy handling and convenient access

– Roses and carnations

Cut Flower Beds

Height dependent• Trellises require bracing to

support weight– Greenhouse structure not

the best choice– Adds to the dead load of

the structure

Cut Flower Beds

Height dependent• Climbing or vine crops use

vertical netting or frames– Sweet peas– Tomatoes– Stephanotis

Cut Flower Beds

Width dependent• Consider the length of a

worker’s reach• Accessible from both sides -

42 in.

• Accessible from one side -18-20 in.

Advantages• Cheapest construction• Long term installation• Easily modified for

organic production• Easily modified for other

crops

Disadvantages• Requires soil amendment• Root spread not

contained• Exposure to potential

pathogens in soil• Drainage tiles may be

required• May result in non-point

source pollution

Construction - Cut Flower Beds

Growing directly in the ground

Construction - Cut Flower Beds

• Isolate from native soil– Prevent root spread– Prevent pathogen exposure– Prevent co-mingling of roots

Construction - Cut Flower Beds

• Amended soil• Native soil • Gravel drainage• Drainage tile

Typical ground bed

Construction - Cut Flower Beds

• Amended soil• Perched water table• Interface must be at

saturation in order for profile to drain

Perched water table

Construction - Cut Flower Beds

• Soil-borne disease• Concrete prevents root

egress• Drain tile to remove excess

water• Pasteurization• Raised edge to prevent

debris

Concrete ground bed

Construction - Cut Flower Beds

• Run beds the length of the greenhouse

• Narrow walks (18”) allows for 67% space use

• Orient north to south to maximize light penetration

Cut flower beds

Benches, Beds and Floors

Function Defines Structure• Potted Crops and Bedding Plants

– Raised benches– Ebb and Flood (flow) tables– Trough systems– Flood floor systems

Benches - Potted Crops

• Raised benches• Height should be adapted to worker height – 32 to

36 inches high– Width

• One side - do not exceed 3 feet• Two sides - do not exceed 6 feet• Wider widths reduce labor efficiency

Benches - Potted Crops

• Air circulation– Bench top material must allow for air circulation– Bench top material must allow for water drainage– No sides

• Reduces labor efficiency forcing a worker to lift a pot or tray over an edge

• Reduces air circulation

Benches - Potted Crops

Benches - Potted Crops

• Construction Materials– Wire mesh or expanded steel (galvanized)– Redwood lath– Bench tops may be supported by concrete blocks, wood

framing or steel framing– Provide support to prevent sagging

Benches - Potted Crops

• Peninsular layout– 80% of space use

• Benches typically run across width of greenhouse

• Aisles 18 in. wide• Center aisle

– 3-4 feet for carts– 8 foot for vehicles or larger

transport systems

Fixed Bench Tops

Fixed Bench Tops

Under Bench Area Important

Benches - Potted Crops

• Moveable benches– 90% or more space use– One aisle, several benches – Each bench allowed to

move opening a space

Rolling Top Benches

Rolling Top Benches

Rolling Top Benches

Moving Benches

• Bench moves on trolley• Bench moves in and out of greenhouse• Benches moved to worker for plant handling• Adaptable to high degrees of automation

– High initial investment– low labor input

Moving Benches

Moving Benches

Ebb and Flood Tables and Floors

• Water tight benches allowing periodic flooding with water and fertilizer

• Trough systems– a modification of water tight benches where narrow troughs

are used to hold plants for periodic flooding with water and fertilizer, allowing air circulation

Ebb and Flood Tables

Ebb and Flood Tables

Ebb and Flood Tables and Floors

• Flood floor systems– Floors designed for periodic flooding with water and

fertilizer– Closed system preventing waste and point source pollution

• Water• Nutrients• Pesticides

Capillary Mat Tables

Flood Floors

Floor Production

Floor Production

Hanging Basket Lines

Hanging Basket Lines